Analysis of NMR line shapes of rigid-lattice multispin systems. IV. 19F shielding tensors of trifluoromethyl halides

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Abstract
The principal elements of the fluorine chemical shift and spin‐rotation tensors and their directions in the molecular coordinate system have been determined for CF3X molecules (X = F, Cl, Br, I) from analysis of low‐temperature rigid‐lattice NMR line shapes of these molecules enclathrated in D2O. In general, the shielding tensors are not axially symmetric, in disagreement with the assumption of axial symmetry commonly used to interpret liquid crystal results. The shielding tensor values in trifluoromethyl halides appear to be dominated by the electron currents induced by the mixing of the highest occupied nonbonding 2p orbitals on the fluorine atoms with low‐lying unoccupied orbitals of the C–X bond under the influence of the magnetic field.